As the reserves of conventional crude oils decline, heavy oils must be upgraded to meet demands for gasoline, diesel fuel, and other fuels. In upgrading these heavy oils, the heavier materials are converted to lighter fractions and most of the sulfur, nitrogen, carbon residue and metals must be removed. Crude oil is typically first processed in an atmospheric crude distillation tower to provide fuel products including naphtha, kerosene and diesel. The atmospheric crude distillation tower bottoms stream is typically taken to a vacuum distillation tower to obtain vacuum gas oil (VGO) that can be feedstock for an FCC unit or other uses. VGO typically boils in a range between at or about 300° C. (572° F.) and at or about 524° C. (975° F.).
Heavy oils include materials such as petroleum crude oil, atmospheric tower bottoms products, vacuum tower bottoms products, heavy cycle oils, shale oils, coal derived liquids, crude oil residuum, topped crude oils and the heavy bituminous oils extracted from oil sands which contain greater than 5 wt % material boiling at a temperature higher than 524° C. and preferably greater than 25 wt % material boiling at a temperature higher than 524° C. Of particular interest are the oils extracted from oil sands and which contain wide boiling range materials from naphthas through kerosene, gas oil, pitch, etc., and which contain a large portion, i.e. greater than 75%, of material boiling above 524° C. These heavy hydrocarbon feedstocks may be characterized by low reactivity in visbreaking, high coking tendency, poor susceptibility to hydrocracking and difficulties in distillation. Most residual oil feedstocks which are to be upgraded contain some level of asphaltenes which are typically understood to be heptane insoluble compounds as determined by ASTM D3279 or ASTM D6560. Asphaltenes are high molecular weight compounds containing heteroatoms which impart polarity.
Heavy oils are known to contain a variety of carbon residue contaminants. The presence of carbon residue in heavy oils during subsequent processing may cause environmental pollution, and may poison the catalysts used. The carbon residue in the heavy oils tends to concentrate in the heavier hydrocarbon fractions, and these heavier fractions including resid and gas oils are normally treated to reduce the carbon residue content. Carbon residue contaminants may also be removed by adsorption onto solid particles such as catalysts or adsorbents. Such particles may be used in conjunction with hydrotreating processes that also reduce the carbon residue content of the heavier hydrocarbon fractions.
Heavy oils must be upgraded in a primary upgrading unit before it can be further processed into usable products. Primary upgrading units known in the art include, but are not restricted to, coking processes, such as delayed or fluidized coking, and hydrogen addition processes such as ebullated bed or slurry hydrocracking (SHC). As an example, the yield of liquid products, at room temperature, from the coking of some Canadian bitumens is typically about 55 to 60 wt % with substantial amounts of coke as by-product. On similar feeds, ebullated bed hydrocracking typically produces liquid yields of 50 to 55 wt %. U.S. Pat. No. 5,755,955 describes a SHC process which has been found to provide liquid yields of 75 to 80 wt % with much reduced coke formation through the use of additives. Slurry hydrocracking (SHC), one such primary upgrading process, is used for the primary upgrading of heavy hydrocarbon feedstocks obtained from the distillation of crude oil, including hydrocarbon residues or gas oils from atmospheric column or vacuum column distillation. In SHC, these liquid feedstocks are mixed with hydrogen and solid catalyst particles, e.g., as a particulate metallic compound such as a metal sulfide, to provide a slurry phase. Representative SHC processes are described, for example, in U.S. Pat. No. 5,755,955 and U.S. Pat. No. 5,474,977. SHC produces naphtha, diesel, gas oil such as VGO, and a low-value, refractory pitch stream. The VGO streams are typically further refined in catalytic hydrocracking or fluid catalytic cracking (FCC) to provide saleable products. To prevent excessive coking in the SHC reactor, heavy VGO (HVGO) can be recycled to the SHC reactor.
The naphtha, diesel oil and vacuum gas oils that are produced by SHC or other primary upgrading processes are some of the intermediate products that require further processing. They have impurities that include high nitrogen (compounds), metal, carbon residue and sulfur (including sulfur compounds) levels. Carbon residue compounds, in particular, are difficult to remove by hydrotreating due to their high levels of aromaticity. Carbon residue materials are generally thought to form detrimental coke deposits on the catalyst and in the reactor. It has now been found that treatment with certain ionic liquids can reduce the level of carbon residue compounds by from a small amount just above 0% and up to 100% depending upon the ionic liquid used and the number of ionic liquid treatments that are done. Carbon residue, sulfur and metals can also be reduced. Following the removal of these impurities, the intermediate products can undergo downstream processing such as hydroprocessing, hydrocracking, fluid catalytic cracking (FCC), blending, platforming and other processes as known to one skilled in the art.